1. Field of the Invention
The present invention generally relates to a semiconductor device, and especially relates to a semiconductor device equipped with an integrated circuit including a metal thin-film-resistor.
2. Description of the Related Art
In an analog integrated circuit, resistors are abundantly used as important components. In recent years and continuing, resistors consisting of a metal thin film (henceforth a metal thin-film-resistor) attract attention in view of low temperature dependency (henceforth TCR) of the resistance. As a material of the metal thin-film-resistors, chromium silicon (CrSi), nickel chromium (NiCr), tantalum nitride (TaN), chromium silicide (CrSi2), chromium silicide nitride (CrSiN), chromium silicon oxy (CrSiO), etc., are used.
It is often the case that the metal thin-film-resistor object of a semiconductor device is formed in the film thickness of less than 100 nm (1000 Å (angstrom)) in order to obtain a high sheet resistance such that requirements for high integration are met.
Conventional methods of obtaining an electrical connection of the metal thin-film-resistor object are as follows.
Method (1): A method of directly connecting metal wiring to the metal thin-film-resistor object (for example, Patent Reference 1).
Method (2): A method of connecting metal wiring through a hole that is formed in a layer insulation film, which hole is formed after forming the metal thin-film-resistor object (for example, Patent Reference 2 and Patent Reference 3).
Method (3): A method of connecting metal wiring to a barrier film that is formed on a metal thin film resistor layer (for example, Patent Reference 4 and Patent Reference 5).
Method (4): A method of forming an electrode inside a connection hole formed in an insulator layer, forming a resistor film on the insulator layer, and then forming a resistor pattern that is connected to the electrode by dry etching (for example, Patent Reference 1).
The foregoing Methods (1) through (4) are further described.
With reference to FIG. 37, Method (1) is described.
A device separating oxide film 3, a transistor (not illustrated), etc. are formed on a silicon substrate 1 that is in the shape of a wafer. Then, a first layer insulation film 5 is formed, and a metal thin-film-resistor object 101 is formed on the first layer insulation film 5. A metal film for wiring is formed all over the first layer insulation film 5 and the metal thin-film-resistor object 101. The metal film for wiring is patterned by a wet etching process, and a first layer metal wiring pattern 103 is formed.
In a manufacturing process of common semiconductor devices, dry etching technology is generally used when etching a metal film for wiring. However, since the metal thin-film-resistor object 101, which is thin, is present directly under the metal film for wiring, over-etching (excessive etching) may take place if the dry etching technology is used. For this reason, it is necessary to use the wet etching technology for patterning the metal film for wiring when forming the first layer metal wiring pattern 103.
Method (2) is described with reference to FIG. 38.
The device separating oxide film 3, the first layer insulation film 5, and the metal thin-film-resistor object 101 are formed on the silicon substrate 1. Then, a CVD (chemical vapor deposition) oxide film 105 serving as a layer insulation film for the metal wiring is formed on the first layer insulation film 5 and the metal thin-film-resistor object 101. A resist pattern for forming a connection hole for metal wiring is formed, the resist pattern having openings that expose the CVD oxide film 105 at both ends of the metal thin-film-resistor object 101. Then, the wet etching technology is carried out with the resist pattern serving as a mask such that connection holes 107 are formed by selectively removing the CVD oxide film 105. Then, the resist pattern is removed, a metal film for wiring, which consists of an AlSiCu film, is formed on the CVD oxide film 105 including the inside of the connection holes 107, patterning of the metal film for wiring is carried out, and a first layer metal wiring pattern 109 is formed.
In a manufacturing process of common semiconductor devices, dry etching technology is used when forming a connection hole. However, where the metal thin-film-resistor object 101 is thinner than 100 nm (1000 Å), it is difficult to prevent the connection holes 107 from running through the metal thin-film-resistor object 101. For this reason, it is necessary to use the wet etching technology when forming the connection holes 107.
Method (3) is described with reference to FIG. 39.
The device separating oxide film 3, the first layer insulation film 5, and the metal thin-film-resistor object 101 are formed on the silicon substrate 1. Then, on the first layer insulation film 5 including the metal thin-film-resistor object 101, a high melting point metal film, such as a TiW film, to serve as a barrier film to the metal wiring is formed, on which a metal film for wiring is formed. Then, the metal film for wiring is patterned using dry etching technology, and the first layer metal wiring pattern 111 is formed. Since the metal film for wiring is formed on the high melting point metal film, the dry etching technology can be used without etching the metal thin-film-resistor object 101. Then, the high melting point metal film is selectively removed by wet etching technology using the first layer metal wiring pattern 111 as a mask, and the high melting point metal film pattern 113 is formed. Here, since the high melting point metal film is formed immediately above the metal thin-film-resistor object 101, patterning of the high melting point metal film by dry etching technology is difficult.
Method (4) is described with reference to FIG. 40.
The first layer insulation film 5 and the device separating oxide film 3 are formed on the silicon substrate 1, and a first layer metal wiring pattern 115 is formed on the first layer insulation film 5. Then, an insulator layer 117 is formed on the first layer insulation film 5 and the first layer metal wiring pattern 115, and first connection holes 119 are formed in the insulator layer 117 on the first layer metal wiring pattern 115 at positions corresponding to both ends of the metal thin-film-resistor object 101. A conductive material is embedded in the first connection holes 119 such that conductive plugs (electrodes) 121 are formed. At this juncture, a connection hole for electrically connecting the first layer metal wiring pattern 115 and a second layer metal wiring pattern 129 formed at a later process is not formed. Next, on the surface of the insulator layer 117 a metal thin film is formed, which is then patterned such that the metal thin-film-resistor object 101 is formed on the conductive plugs 121 and the insulator layer 117.
Then, an insulator layer 123 is formed on the whole surface of the insulator layer 117 so that the metal thin-film-resistor object 101 is prevented from being etched when patterning the second layer metal wiring pattern at a later process using dry etching technology. A second connection hole 125 is formed through the insulator layers 117 and 123 on the first layer metal wiring pattern 115 at a place different from the formation region of the metal thin-film-resistor object 101, the second connection hole 125 being arranged for electrically connecting the second layer metal wiring pattern 129 and the first layer metal wiring pattern 115. A conductive material is embedded in the second connection hole 125, and a second conductive plug 127 is formed. A metal film for forming a second layer metal wiring pattern 129 is formed on the insulator layer 123 including the formation region of the second conductive plug 127, the metal film is patterned by a photoengraving process and a dry etching process, and the second layer metal wiring pattern 129 is formed on the second conductive plug 127 and the insulator layer 123.
Further, although it is not a metal thin-film-resistor object, a semiconductor integrated circuit device equipped with a resistor that is formed on the uppermost layer wiring electrode through an insulator layer and is connected to the uppermost layer wiring electrode is disclosed (for example, Patent Reference 6).
With reference to FIG. 41, the case where such a structure is applied to a metal thin-film-resistor object is described.
The first layer insulation film 5 and the device separating oxide film 3 are formed on the silicon substrate 1, and the first layer metal wiring pattern 115 is formed on the first layer insulation film 5. Then, an underground insulator film 131 is formed on the first layer insulation film 5 including the first layer metal wiring pattern 115. A connection hole 133 is formed to the underground insulator film 131 on the first layer metal wiring pattern 115 by a photoengraving process and a dry etching process. Then, a metal thin film for forming the metal thin-film-resistor object 101 is formed on the underground insulator film 131 including the formation region of the connection hole 133, which metal thin film is patterned to a predetermined form, and the metal thin-film-resistor object 101 is formed.
Further, as a semiconductor device equipped with a metal thin-film-resistor object, an integrated circuit that mounts a metal thin film resistor on an insulation layer of the semiconductor integrated circuit is indicated, wherein the metal thin film resistor contacts metal wiring through an electrode portion of the metal thin film resistor through at least a part of an end and an upper surface of the metal wiring (for example, Patent Reference 7).
With reference to FIG. 42, a method of taking the contact of the metal thin film resistor and the metal wiring through at least a part of the end and the upper surface of metal wiring is described.
The first layer insulation film 5 is formed on the silicon substrate 1 on which the device separating oxide film 3 is formed, and the first layer metal wiring pattern 115 is formed on the first layer insulation film 5. Then, a plasma nitride film 135 is formed on the first layer insulation film 5 including the first layer metal wiring pattern 115. Then, a part of the plasma nitride film 135 is removed so that a part of the ends and the upper surface of the first layer metal wiring pattern 115 are exposed. Then, a metal thin film for forming a metal thin film resistor is deposited, which is then patterned, and the metal thin-film-resistor object 101 is formed.
Further, after a semiconductor device is physically structured, a laser trimming process is performed, wherein a laser beam is irradiated onto certain elements such as a fuse element and a resistor in order to disconnect or modify the elements for adjustment of the performance of the semiconductor device (for example, Patent Reference 8).
However, when the laser beam is irradiated in the laser trimming process, the laser beam may penetrate insulator layers, such as the oxidization silicon film, and may be irradiated onto the semiconductor substrate, for example, a silicon substrate. That may cause damage to the silicon substrate, and the reliability of the semiconductor device may be degraded, which is a problem. Further, in an online trimming process, wherein trimming is performed while measuring the performance of the semiconductor device, when a laser beam is irradiated onto the silicon substrate, an electron hole pair is produced in the silicon substrate. The electron hole pair generates noise that hinders correct measurement, and precise trimming cannot be obtained, which is a problem.
In order to cope with the problems, the following methods are proposed; namely, a method of arranging a coat around a resistor for preventing penetration of the laser beam (for example, Patent Reference 9), and a method of arranging a laser-beam shielding object consisting of one of polysilicon, a high melting point metal, and a silicide of high melting point metal between the fuse that consists of polysilicon and the silicon substrates (for example, Patent Reference 10).
Further, Patent Reference 11 discloses a method of stabilizing energy actually absorbed by the metal thin-film-resistor object in the case of the laser trimming process by forming a lower layer and an upper layer of a metal thin-film-resistor object by silicon oxide films of predetermined thickness. According to the Patent Reference 11, a silicon oxide film (SiO2), a PSG (phospho silicate glass) film, and a BPSG (borophospho silicate glass) film are indicated as the silicon oxide film for the lower layer and the upper layer of the metal thin-film-resistor object.
[Patent Reference 1] JPA 2002-124639
[Patent Reference 2] JPA 2002-261237
[Patent Reference 3] Japanese Patent No. 2699559
[Patent Reference 4] Japanese Patent No. 2932940
[Patent Reference 5] Japanese Patent No. 3185677
[Patent Reference 6] JPA 58-148443
[Patent Reference 7] JPA 61-100956
[Patent Reference 8] JPA 8-124729
[Patent Reference 9] JPA 56-58256
[Patent Reference 10] JPA 58-170
[Patent Reference 11] Japanese Patent No. 2536303